1. Field of the Invention
The present invention relates to a float-operated over-center valve actuating mechanism for a liquid pumping system where a pressure vessel is alternately filled with a liquid and emptied with pump operation controlled by the liquid level within the pressure vessel. More particularly, it relates to a liquid pumping system which incorporates a vapor trap within the vessel on the liquid outlet line.
2. The Prior Art
Over-center float-operated valve actuating mechanisms are known, for example from U.S. Pat. No. 5,141,405 to Francart Jr. Such over-center float-operated valve actuating mechanisms are useful in controlling the filling of a closed or sealed pressure vessel. The vessel includes a vent valve for venting the steam or vapor and a second pressure valve subjected to high pressure inlet fluid, such as live steam at 100-500 psi, to drive an accumulated liquid periodically from the vessel.
During filling of the vessel, the vent valve is in the open position and the pressure valve is closed by the over-center float-operated valve actuating mechanism. As the vessel fills with liquid, the float-operated valve actuating mechanism snaps quickly through the center position, closing the vent valve and simultaneously opening the high pressure inlet valve to pump the accumulated liquid from the vessel. When the liquid level drops below a predetermined level, the float-operated valve actuating mechanism snaps quickly through the center position, opening the vent valve and simultaneously closing the high pressure inlet valve.
A check valve at the liquid outlet opening is ordinarily closed by a liquid outlet pressure which is greater than the liquid inlet pressure. However, a deficiency exists with the prior art automatic pumps, whereby live steam or process gas will pass through the liquid outlet opening when the liquid inlet pressure exceeds the liquid outlet pressure. Therefore, it would be advantageous to provide an automatic liquid pump that prevents the loss of vapor from the pressure vessel when the liquid inlet pressure is greater than the liquid outlet pressure.